This invention overcomes the failings of the processes of the prior art and in particular contributes to:                reducing emissions enriched in carbon monoxide        reducing the consumption of coke for the blast furnace        increasing the productivity of the blast furnace        simplifying the rotating machines of the appliance        facilitating regulation        preventing a deterioration in the energy consumptionfor a process for capturing CO2 on a ferrous metallurgy unit, optionally with recycling.        
As the compressor upstream of the adsorption unit operates at a substantially constant compression ratio, if the pressure of the waste gas from the ferrous metallurgy unit varies, this results in a reduction in pressure upstream of the adsorption unit. The process according to the invention makes it possible for the adsorption unit to be able to accept these different inlet pressures with a good intrinsic output for the CO and an overall output for CO of approximately 100%, by virtue in particular of the recycling gas.
The fluid enriched in carbon dioxide comprises, for example, at least 70 mol % of carbon dioxide and can be in the gaseous or liquid form.
It is known, from WO-A-2006/106253, to use an adsorption process, followed by a process for purification by distillation, to produce a gas enriched in carbon dioxide and a waste gas enriched in carbon monoxide.
FR-2 848 123 describes a process for the separation of a waste gas from a ferrous metallurgy unit by washing with amines. The processes for washing with amines cannot function with a feed flow of variable pressure.
US2003/0047037 describes a process for the separation of a waste gas from a ferrous metallurgy unit by adsorption, using a purging gas which is natural gas and producing solely flows intended to be mixed with natural gas and sent to the ferrous metallurgy unit.
The invention provides for the recycling of a portion or all of the decarbonated gas enriched in carbon monoxide originating from the blast furnace. This process makes it possible specifically to reduce consumptions of coke per tonne of cast iron but also offers the advantage of increasing the productivity of the blast furnace.
The waste gas originating from the blast furnace has a pressure which can vary as a function of the charging rate of the plant. These variations are typically greater than 1 bar, which is not acceptable by current technologies for commercial machines while maintaining a constant discharge pressure towards the PSA. It should be noted that the pressure of the blast furnace and the molar flow of the waste gas vary substantially proportionally, resulting in a virtually constant flow by volume at the suction of the machine for compressing the blast furnace gas.